Late last week on the way home I suddenly got the message "AC off due to high engine temp" message, and the temp gauge starting spiking. I had just checked the coolant level the day before and it was fine, but turned the heat and fan on high and pulled over as quick as I could and checked the level. It was low. I added coolant, as then started up the Cruze, and checked the temperature. The gauge went back down so I started driving again.
I kept monitoring the temperature display, as I have the digital readout, my Cruze being a 2012. Driving temperature was now running low, in the 150 degree range and it wouldn't go any higher.
What I think happened is the thermostat got stuck closed, blew off a bunch of coolant out of the coolant reservoir, and then somehow the thermostat got stuck open. Whether this was by accident, or by design to protect the engine, I don't know.
I bought a new thermostat and replaced it over the weekend. Today, I monitored the coolant temp all day, driving about 200 miles for work, and noticed something different. Coolant level is still fine, but my normal "high" coolant temperature is now 195 to 200 degrees. If I really push it, I can get it as high as 207. Normal operating temperature used to be in the 210 to 220 degree range.
I researched the thermostat part numbers, and as far as I can tell, the part number has changed. It used to be part number 55579010, and now it is 55593034. What is going on here? As I understood it, the thermostat is electronically controlled, so why did my "normal" coolant temperature change?